1. Field
The present invention is concerned with novel compounds containing a cyclohexyl alkenoate residue, liquid crystalline mixtures containing such compounds, and the use of such compounds and mixtures for electro-optical purposes.
2. Description
Liquid crystals are used primarily as dielectrics in indicating devices, since the optical properties of such substances can be influenced by an applied voltage. Electro-optical devices based on liquid crystals are well-known and can employ various effects. Such devices are, for example, dynamic scattering cells, DAP cells ("deformation of aligned phases"), guest/host cells, TN cells ("twisted nematic" structure), STN cells ("super twisted nematic"), SBE cells ("super birefringence effect") and OMI cells ("optical mode interference"). Most common indicating devices are based on the Schadt-Helfrich effect and have a twisted nematic structure.
Liquid crystal materials should have good chemical and thermal stability as well as stability towards electric fields and electromagnetic radiation. At usual operating temperatures they should have a suitable mesophase, for example a nematic, cholesteric or tilted smectic phase. Moreover, liquid crystal materials should have low viscosity and, when used in cells, should give short response times, low threshold potentials and high contrast.
Other properties such as electrical conductivity, dielectric anisotropy and optical anisotropy must fulfill various requirements depending on the type of cell and field of application. For example, materials for cells having a twisted nematic structure should have positive dielectric anisotropy and minimal electrical conductivity. In addition to the general interest in liquid crystal materials having high optical anisotropy, there has recently been increased interest in materials exhibiting low optical anisotropy, especially for actively addressed liquid crystal displays, e.g. for TFT applications ("thin film transistor") in television sets.
Liquid crystals are typically used as mixtures of several components to optimize properties. It is therefore important that the components are readily miscibility.
Such compounds are provided by the present invention.